1. Field of the Invention
The present invention relates to a stereoscopic image display technique. More specifically, the present invention relates to a stereoscopic image display device and the like for converting an image to a stereoscopic image with which an observer does not feel a sense of discomfort even when the observer changes one's position.
2. Description of the Related Art
Recently, television sets capable of viewing stereoscopic images are on the general market. Accordingly, the amount of the stereoscopic image contents is increased, and the environments for viewing the stereoscopic images are coming to be in good condition. In general, the observer wears eyeglasses for stereoscopic image display to project images of different parallaxes on left and right eyes so that the observer can view the stereoscopic image on the stereoscopic image television set. However, there are many observers who feel a sense of displeasure to wear the eyeglasses for stereoscopic image display, and a stereoscopic image display device that requires no such eyeglasses is desired. Further, when the eyeglass-type stereoscopic image display device is utilized as a mobile device, it is inconvenient since the stereoscopic image display device and the eyeglasses for stereoscopic image display are required to be carried to the outside. Thus, such stereoscopic image display device that requires no eyeglasses is more strongly desired for mobile use.
As the stereoscopic image display that requires no eyeglasses for stereoscopic image display, generally used is a type which divides spatial areas for projecting a stereoscopic image, and projects images of different parallaxes to each of the divided spatial areas so as to project images of different parallaxes to the left and right eyes of the observer. Through providing a lenticular lens and a parallax barrier on a stereoscopic display panel of the stereoscopic display device, the images of different parallaxes are provided for each of the divided spatial areas.
With such-type of stereoscopic image display device, it is not necessary to wear the eyeglasses for stereoscopic image display. Thus, it is excellent in terms of avoiding such trouble of wearing eyeglasses and is expected to be utilized in mobile use in particular. However, images of different parallaxes are projected by being spatially isolated with such type, so that the spatial area where the observer can visually recognize the stereoscopic images properly becomes limited. The spatial area where the observer can visually recognize the stereoscopic images properly is limited to a case where the position of the left eye of the observer is within the spatial area where the left-eye image is projected and the position of the right eye of the observer is within the spatial area where the right-eye image is projected. When the positions of the left and right eyes of the observer are shifted from those spatial areas, the left-eye image and the right-eye images may be viewed by being overlapped on one another (viewed as a CT-image) or a video of inverted sense of depth (so-called pseudoscopic view) may be viewed by the observer.
Now, the spatial area divided by a stereoscopic panel will be described by referring to the accompanying drawings. First, the spatial area in a case where a parallax barrier is used as the stereoscopic display panel will be described.
FIG. 64 shows an example of an optical model in which images of different parallaxes are projected to the left and right eyes of an observer with the parallax-barrier type stereoscopic image display device. FIG. 64 is a sectional view observed from the above the head of the observer, in which the both eyes (right eye 55R and left eye 55L) of the observer are located on an observing plane 30 distant by an optimum observing distance OD from the display plane of the display device, and the center of the both eyes of the observer and the center of the display panel match with each other.
The image display panel (not shown) is constituted with a group of optical modulators that are pixels arranged in matrix (e.g., a liquid crystal panel). In FIG. 64, among the right-eye pixels 4R and the left-eye pixels 4L arranged alternately, only each of the pixels at both ends of the image display panel and in the center are illustrated. A parallax barrier 6 that functions as a means for dividing a spatial area and projecting images is disposed on the far side of the display panel from the observer. The parallax barrier 6 is a barrier (a light shielding plate) on which a great number of thin vertical striped slits 6a are formed, and it is disposed in such a manner that the longitudinal direction of the barrier itself becomes orthogonal to the direction along which the left-eye pixels 4L and the right-eye pixels 4R of the image display panel are arranged. In a still far side of the parallax barrier, a light source (not shown: so-called backlight) is placed. Light emitted from the light source transmits through the slits 6a and is projected towards the observer while the intensity thereof is being modulated in the pixels within the image display panel. The projecting directions of the right-eye pixel 4R and the left-eye pixel 4L are limited by the existence of the slits 6a. 
When a locus of the light passing through the closest pixel among the light emitted from each of the slits 6a is illustrated as a light ray 20, a right-eye area 70R (a spatial area where the right-eye image is projected) where the projection images of all the right-eye pixels 4R are superimposed and a left-eye area 70L (a spatial area where the left-eye image is projected) where the projection images of all the left-eye pixels 4L are superimposed can be acquired. Only the projection images from the right-eye pixels 4R can be observed in the right-eye area 70R, and only the projection images from the left-eye pixels 4L can be observed in the left-eye area 70L. Therefore, when the parallax images are projected to the left and right eyes while the right eye 55R of the observer is located within the right-eye area 70R and the left eye 55L is located within the left-eye area 70L, the observer visually recognizes those as a stereoscopic image. In other words, the observer can observe a desired stereoscopic image when the right eye 55R is located within the right-eye area 70R and the left eye 55L is located within the left-eye area 70L. The display device shown in FIG. 64 is so designed that the projection images (width P′) at the optimum observing distance OD of each of the right-eye pixel 4R and the left-eye pixel 4L (width P) all superimpose with each other so that the width of the right-eye area 70R and the left-eye area 70L becomes the maximum on the observing plane 30. The width P′ of the projection image is mainly determined based on the distance h between the slit 6a and the pixel, the pixel pitch P, and the optimum observing distance OD. When the width P′ is widened, the width of the right-eye pixel 70R and the left-eye pixel 70L is widened. However, it is impossible to locate each of the both eyes of the observer at arbitrary positions, so that the stereoscopic area where the stereoscopic images can be sighted cannot necessarily be expanded. Provided that the distance between both eyes is e, it is preferable to design the width P′ to be equivalent to the space e between the both eyes. In a case where the width P′ is smaller than the space e between the both eyes, the area of stereopsis is limited to the width P′. In the meantime, in a case where the width P′ is larger than the space e between the both eyes, the area where the both eyes are located in the right-eye area 70R or the left-eye area 70L is simply increased. Note that a slit width S is written in FIG. 64.
Further, FIG. 65 shows an optical model of a case where the parallax barrier 6 is disposed on the front side of the display panel when viewed from the observer. As in the case where the barrier is disposed on the far side of the display panel when viewed from the observer, the observer is at the optimum observing distance OD, and the projection images (width P′) of each of the left-eye and right-eye pixels (width P) are designed to superimpose with each other on the observing plane 30. When a locus of the light passing through the closest slit 6a among the light emitted from each of the pixels is illustrated as the light ray 20, the right-eye area 70R where the projection images of all the right-eye pixels 4R are superimposed and the left-eye area 70L where the projection images of all the left-eye pixels 4L are superimposed can be acquired.
Next, FIG. 66 shows spatial areas divided when a lenticular lens is used instead of the parallax barrier. In FIG. 66, the parallax barrier 6 of FIG. 65 is simply changed to the lenticular lens 3. Next, a case where the observer is located in a pseudoscopic viewing space away from an area (a stereoscopic viewing space) where the observer can visually recognize a stereoscopic image properly will be studied by using the lenticular-lens type optical model. FIG. 67 is a sectional view when observed from above the head of the observer in a case where the observer moves to the right side so that the right eye 55R moves out of the right-eye area 70R into the left-eye area 72L and the left eye 55L moves out of the left-eye area 70L into the right-eye area 70R.
In this case, the light rays 20 passing through the principal point (vertex) of the closest cylindrical lens 3a among the light emitted from the left-eye pixels 4L and the right-eye pixels 4R do not reach the position of the right eye 55R of the observer. However, when a light ray passing through the principal point (vertex) of the second closest cylindrical lens 3b among the light emitted from the left-eye pixels 4L is illustrated as a light ray 21, the second left-eye area 72L can be acquired. That is, in FIG. 67, the observer observes the projection image from the left-eye pixel 4L by the right eye 55R and observes the right-eye pixel 4R by the left eye 55L. Thus, when a stereoscopic image is observed, the popup image and the depth image are presented in an inverted manner (so-called pseudoscopic view). Therefore, a desired stereoscopic image cannot be sighted. Note here that the right-eye area 70R is the stereoscopic viewing space for the right eye 55R, and the left-eye areas 70L and 72L are the pseudoscopic viewing spaces. In the meantime, the left-eye areas 70L, 72L are the stereoscopic viewing spaces for the left eye 55L, and the right-eye area 70R is the pseudoscopic viewing space.
Next, a case where the observer is located in a 3D-crosstalk viewing space away from an area (a stereoscopic viewing space) where the observer can visually recognize a stereoscopic image properly will be studied by using the lenticular-lens type optical model. FIG. 68 is a sectional view when observed from above the head of the observer in a case where the observer moves to the right side so that the right eye 55R comes to be located at the boundary between the right-eye area 70R and the left-eye area 72L and the left eye 55L comes to be located at the boundary between the right-eye area 70R and the left-eye area 70L.
In this case, the light ray 20 passing through the principal point (vertex) of the closest cylindrical lens 3a among the light emitted from the right-eye pixels 4R and the light ray 21 passing through the principal point (vertex) of the second closest cylindrical lens 3b among the light emitted from the left-eye pixels 4L are both projected to the position of the right eye 55R of the observer. That is, in FIG. 68, the observer observes the projection images from both the right-eye pixels 4R and the left-eye pixels 4L with the right eye 55R. Thus, when a stereoscopic image is observed, the right-eye pixels 4R and the left-eye pixels 4L are superimposed to produce a CT-image (so-called 3D crosstalk). Therefore, a desired stereoscopic image cannot be sighted. Note here that the area of the boundary between the right-eye area 70R and the left-eye area 72L and the area of the boundary between the right-eye area 70R and the left-eye area 70L are the 3D-crosstalk viewing spaces.
As described above, with the stereoscopic image display device that requires no eyeglasses for stereoscopic image display, issues of having a CT-image and pseudoscopic view occur depending on the observing position of the observer. Therefore, the observer feels a sense of discomfort, which is a reason for preventing the stereoscopic image display devices from being spread.
In order to overcome such issues, there is proposed a method which detects the observing position of the observer, and switches and displays a stereoscopic image having parallax and a flat image having no parallax depending on the position (WO 2010/061689 (Patent Document 1) and Japanese Unexamined Patent Publication 2003-107392 (Patent Document 2)).
Further, also proposed is a method which detects the observing position of the observer, and performs parallax adjustment processing for entirely shifting the images of different parallaxes to display a stereoscopic image with which the load for the observer in a pseudoscopic viewing space is lightened (Japanese Unexamined Patent Publication 2012-010084 (Patent Document 3)). Further, also proposed are methods which detect the observing position of the observer and change the position of a parallax barrier for taking the countermeasure for the issues of CT-image by 3D crosstalk and pseudoscopic view (Japanese Unexamined Patent Publication 2000-152285 (Patent Document 4), Japanese Unexamined Patent Publication 2007-318184 (Patent Document 5), Japanese Unexamined Patent Publication 2010-014891 (Patent Document 6), Japanese Unexamined Patent Publication 2012-039469 (Patent Document 7), and Jung-Min Choi, et al “Autostereoscopic 3D with Wide Viewing Angle using Gyro-Sensor,” IDW11 3Dp-7, pp. 291-294 (Non-Patent Document 1)). Among those, Patent Document 7 proposes a method which performs parallax adjustment processing on the images of different parallaxes to express motion parallax with which an object within a stereoscopic image moves in association with the move of the observer.
Further, there is proposed a method which expresses motion parallax even in a normal image display device by detecting the observing position of the observer, converting images to the image information of the viewpoint which corresponds to the observing position, and displaying it (Japanese Unexamined Patent Publication 2007-052304 (Patent Document 8)).
Further, there is also proposed a method which adjusts the parallax amount by shifting the right-eye image entirely so that the luminance difference between the left-eye image and the right-eye image becomes the minimum, and displays a stereoscopic image so as to reduce the influence of a CT-image by 3D crosstalk thereby (Japanese Unexamined Patent Publication 2010-200123 (Patent Document 9)).
Further, even when stereoscopic image contents of same parallax are displayed, the parallax of the stereoscopic image contents observed by the observer changes depending on the distance between the stereoscopic image display device and the observing position of the observer. There is also proposed a method which displays a stereoscopic image by adjusting the parallax of the stereoscopic image content according to the distance between the stereoscopic image display device and the observing position of the observer in order to overcome such an issue that the stereoscopic image cannot be sighted when the distance between the stereoscopic image display device and the observing position of the observer becomes too close so that the parallax of the stereoscopic image contents becomes too large (Japanese Unexamined Patent Publication 2012-044308 (Patent Document 10)).
Further, also proposed is a method which displays a high-quality stereoscopic image through detecting the observing position and observing angle of the observer with respect to the display unit and adjusting the parallax of the image data according to the observing angle while considering the crosstalk amount by the view-range angle, view-range width, and flank curvature of the stereoscopic image display device (Japanese Unexamined Patent Publication 2012-060607 (Patent Document 11)).
With the naked-eye stereoscopic image display device that requires no eyeglasses for stereoscopic image display, there are issues of a CT-image caused by 3D crosstalk and pseudoscopic view depending on the observing position of the observer. This gives not only a sense of discomfort to the observer but also is one of the factors for causing physiological instability such as feeling video sickness and eye fatigue in a case of a stereoscopic image display device with a low picture quality, which is a reason for preventing the naked-eye stereoscopic image display device from being spread.
As the methods for overcoming such issue, Patent Documents 1 and 2 are proposed. However, the methods of Patent Documents 1 and 2 give a sense of discomfort to the observer with a drastic change in the parallax value where a differential coefficient of the parallax value for the viewing angle becomes almost infinite when switching a stereoscopic image having parallax and a flat image having no parallax.
Patent Document 3 discloses a technique which makes it possible to display a stable stereoscopic image by suppressing a popup amount when the observer stands still, through shifting the parallax image entirely and performing parallax adjustment processing. However, the parallax adjustment processing method disclosed in patent Document 3 cannot overcome the issue of the CT-image by the 3D crosstalk and does not take the shift speed of the observing position of the observer into consideration, so that the observer still feels a sense of discomfort.
Patent Documents 4, 5, 6, 7 and Non-Patent Document 1 propose the techniques which can provide a countermeasure for the issues of the CT-image and the pseudoscopic view by the 3D crosstalk through changing the position of the parallax barrier. However, it is required to have a barrier driving device for changing the position of the barrier with all of the techniques depicted in those documents, so that the device cost is increased. Also, the power consumption is increased, since it can only be applied to the parallax barrier type. Further, while Patent Document 7 proposes a method which expresses motion parallax by performing the parallax adjustment processing, it is not possible with the method to overcome the issue of the CT-image by the 3D crosstalk.
Patent Document 8 proposes a technique which expresses motion parallax through displaying an image by converting it to the image information of the viewpoint according to the observing position. However, the image displaying method of Patent Document 8 does not take the method for displaying a stereoscopic image by binocular parallax into consideration, so that a stereoscopic image content having binocular parallax cannot be displayed (does not consider the issue of a CT-image by 3D crosstalk, either).
Patent Document 9 proposes a method which reduces the influence of a CT-image by the 3D crosstalk through displaying a stereoscopic image by adjusting the parallax amount through shifting the right-eye image entirely. However, when the stereoscopic image is displayed by shifting the right-eye image entirely, a parallax expression different from the original stereoscopic image content is displayed in a part of the image area (e.g., there is a possibility that the image area that is to be popup-displayed may be changed to be depth-displayed by the shift processing performed on the entire image). Further, the method of Patent Document 9 does not use the observing position of the observer and performs the parallax adjustment processing by shifting the image at all times. Therefore, even when the observing position of the observer is within a stereoscopic viewing space, an appealing stereoscopic image content cannot be displayed.
Patent Document 10 proposes a method which performs parallax adjustment processing on the stereoscopic image content according to the distance between the stereoscopic image display device and the observing position of the observer. However, the method of Patent Document 10 does not consider any method for calculating the parallax adjustment amount for lightening the influence of the CT-image by the 3D crosstalk generated in a naked-eye type stereoscopic image display device which spatially separates and projects the right-eye image and the left-eye image by using a lenticular lens or a parallax barrier, so that the issue of the CT-image by the 3D crosstalk cannot be overcome.
Patent Document 11 proposes a method for adjusting the visual field according to the changes in the view-area angle, the view-area width, and the crosstalk amount. However, as a specific processing method, depicted thereon is only the parallax adjustment method which is performed according to the change in the view-area angle and view-area width, and the parallax adjustment method which is performed according to the change in the crosstalk is not depicted. At the same time, the parallax adjustment method of Patent Document 11 does not consider the point regarding the stereoscopic viewing space, the pseudoscopic viewing space, and the 3D-crosstalk viewing space described above so that it is not possible to lighten the influence of the CT-image in the 3D-crosstalk viewing space appearing also in the area where the observing angle θ is sufficiently small and the flank curvature is not generated. Further, with the parallax adjustment processing depicted in Patent Document 11, the parallax value does not take a negative value. Therefore, it is not possible to take a countermeasure even when pseudoscopic view is generated. Furthermore, the parallax adjustment processing depicted in Patent Document 11 does not consider the shift speed of the observing position. Thus, the parallax value is changed drastically when the observing position is shifted at a fast speed, thereby giving a sense of discomfort to the observer.
None of the documents from Patent Documents 1 to 10 and Non-Patent Document 1 proposes a technique which overcomes the issues of the CT-image and the pseudoscopic view by the 3D crosstalk through performing the parallax adjustment processing on the stereoscopic image content by referring to the device characteristic data containing the display characteristic with respect to the viewing angle of the stereoscopic display panel of the stereoscopic image display device.
It is therefore an exemplary object of the present invention to overcome the above-described issues and to provide a stereoscopic image display device and the like with which the issues of the CT-image and pseudoscopic view caused by 3D crosstalk can be overcome without giving a sense of discomfort by the drastic change in the parallax value so that a sense of discomfort is not felt by the observer even when the observing position of the observer is shifted even with the stereoscopic image display device having no barrier driving device.